Mould-pressing machines of the kind referred to above are e.g. known from U.S. Pat. Nos. 5,494,094 and 4,791,974.
In mould-pressing machines of the kind referred to above, usually being adapted to operate automatically producing series of casting moulds or casting-mould parts, it is of crucial importance that the correct quantity of liquid mist be injected in each cycle. Thus, an excess of liquid mist will, in addition to increasing the costs, create an unnecessary load on the environment, while too small quantities of liquid mist will result in an insufficient "lubrication" of the mould-chamber walls, in the worst case possibly causing parts of the compacted object to stick to the patterns mounted on the mould-chamber walls and thus make the mould part unsuitable for pouring.
Thus, it is desirable to inject the least possible quantity of liquid with the liquid mist, while at the same time ensuring with absolute certainty that the mould is lubricated sufficiently.
It is a relatively simple matter to ensure that the quantity being supplied to the system in each operating cycle is held below a predetermined upper limit, this effect e.g. being attainable by means of a suitably time-controlled and cycle-controlled pump only applying pressure to the liquid to be atomized in a period corresponding to the desired quantity of liquid mist for each operating cycle. Thus, the maximum quantity of liquid that it is possible to advance through the liquid path with a given pressure at a given moment in time sets the upper limit for the quantity of liquid.
On the other hand it can, however, be difficult to set the lower limit for the quantity of liquid being supplied to the liquid mist, a number of relationships coming into play. Thus, it is of primary importance that the liquid quantity being supplied is converted into a uniform liquid mist being distributed uniformly on the mould chamber walls, so that a sufficient quantity of liquid will be deposited on these walls to provide the requisite lubrication. If the nozzle aperture or other parts of the nozzle are contaminated by particulate mould material or other particles, this will have a negative effect on the formation of the liquid mist and the quantity of liquid being introduced into the mould chamber.
For this reason, the prior art referred to initially comprises the use of nozzles, in which it is possible to maintain a continuous air stream through the outlet aperture, making it difficult for particles from the mould chamber to penetrate into the apertures.
In these nozzles, the liquid mist is formed by liquid being injected from a first nozzle aperture into a vortex chamber, in which it is mixed with the atomizing air being blown into the vortex chamber from a second nozzle aperture, after which the liquid mist is discharged from the outlet aperture or apertures.
With this known technology, it has been difficult to form a liquid mist with fine and uniform droplets. In the prior art this makes it necessary to supply more liquid to the liquid mist than would have been necessary, if the liquid mist were more uniform and had finer droplets.
Further, it has been necessary to use relatively complex valves for shutting-off the liquid at the first nozzle aperture, because this valve is of substantial importance for the accuracy and precision with which the liquid can be delivered to the vortex chamber. It has, however, frequently been necessary to supply a greater quantity of liquid in order to compensate for inaccuracies and lack of precision in the delivery of the liquid. In addition to this, the possibility of liquid leaks occurring, e.g. due to particles--in spite of the continuous stream of air--having penetrated from the mould chamber and in through the outlet aperture to the shut-off valve at the nozzle aperture, has made it necessary to construct the valve in a complicated manner in order to safeguard the operation, and to supply a greater amount of liquid in order to compensate for possible leaks, respectively.